No period and negative tests.

I was supposed to start my period on October 23rd. I still havent had a period. Ive been cramping here and there since i was to start. Ive taken 2 tests and both were negative. I have REALLY tender breast. The worse ive ever had for a month now. I feel more tired then usual and have been getting dizzy lately. Dr wants me to start taking progresterone. Could i still be pregnant?